Chapter 11 Human Bio

The human male reproductive system consists of a number of sex organs that are a part of the human reproductive process. In the case of men, these sex organs are located outside a man's body, around the pelvic region. The main male sex organs are the penis and the testes which produce semen and sperm, which as part of sexual intercourse fertilize an ovum in a woman's body and the fertilized ovum (zygote) gradually develops into a fetus, which is later born as a child.

Penis Main article: Penis An uncircumcised penis when flaccid and erect . The penis has a long shaft and enlarged tip called the glans penis. The penis is the male copulatory organ. When the male becomes sexually aroused, the penis becomes erect and ready for sexual activity. Erection is achieved because blood sinuses within the erectile tissue of the penis become filled with blood. The arteries of the penis are dilated while the veins are passively compressed so that blood flows into the erectile cartilage under pressure. The male penis is made of two different tissues. Cartilage is not in the penis.

Epididymae Main article: Epididymus The epididymus is a whitish mass of tightly coiled tubes cupped against the testicles. It acts as a storage place for sperm before they enter the vasa deferentia, tubes that carry sperm form the testes to the urethra. TESTES: The testicle (from Latin testiculus, diminutive of testis, meaning "witness" [of virility],[1] plural testes) is the male generative gland in animals. The etymology of the word is based on Roman law. The Latin word "testis", witness, was used in the firmly established legal principle "Testis unus, testis nullus" (one witness [equals] no witness), meaning that testimony by any one person in court was to be disregarded unless corroborated by the testimony of at least another. This led to the common practice of producing two witnesses, bribed to testify the same way in cases of lawsuits with ulterior motives. Since such "witnesses" always came in pairs, the meaning was accordingly extended, often in the diminutive (testiculus, testiculi).[citation needed Function

Like the ovaries to which they are homologous, testes are components of both the reproductive system (being gonads) and the endocrine system (being endocrine glands). The respective functions of the testes are: •

producing sperm (spermatozoa)

•

producing male sex hormones of which testosterone is the best-known

Both functions of the testicle, sperm-forming and endocrine, are under control of gonadotropic hormones produced by the anterior pituitary:

•

luteinizing hormone (LH)

•

follicle-stimulating hormone (FSH)

Layers

Many anatomical features of the adult testis reflect its developmental origin in the abdomen. The layers of tissue enclosing each testicle are derived from the layers of the anterior abdominal wall. Notably, the cremasteric muscle arises from the internal oblique muscle.

Development There are two phases in which the testes grow substantially; namely in embryonic and pubertal age. [edit] Embryonic

During mammalian development, the gonads are at first capable of becoming either ovaries or testes.[7] In humans, starting at about week 4 the gonadal rudiments are present within the intermediate mesoderm adjacent to the developing kidneys. At about week 6, sex cords develop within the forming testes. These are comprised of early Sertoli cells that surround and nurture the germ cells that migrate into the gonads shortly before sex determination begins. In males, the sex-specific gene SRY that is found on the Y-chromosome initiates sex determination by downstream regulation of sex-determining factors, (such as GATA4, SOX9 and AMH), which leads to development of the male phenotype, including directing development of the early bipotential gonad down the male path of development. [edit] Pubertal

The testes grow in response to the start of spermatogenesis. Size depends on lytic function, sperm production (amount of spermatogenisis present in testis), interstitial fluid, and Sertoli cell fluid production. After puberty, the volume of the testes can be increased by over 500% as compared to the pre-pubertal size.[citation needed] Testicles are fully descended before one reaches puberty. EPIDIDYMIDES: The epididymis (pronounced /ɛpɨˈdɪdɨmɪs/, plural: epididymides /ɛpɨˌdɪdɨ ˈmiːdiːz/) is part of the male reproductive system and is present in all male mammals. It is a narrow, tightly-coiled tube connecting the efferent ducts from the rear of each testicle to its vas deferens.

Regions The epididymis can be divided into three main regions •

The head (Caput). The head of the epididymis receives spermatozoa via the efferent ducts of the mediastinum of the testis. It is characterized histologically by a thin myoepithelium. The concentration of the sperm here is dilute.

•

The body (Corpus)

•

The tail (Cauda). This has a thicker myoepithelium than the head region, as it is involved in absorbing fluid to make the sperm more concentrated.

Role in storage of sperm and ejaculation

Spermatozoa formed in the testis enter the caput epididymis, progress to the corpus, and finally reach the cauda region, where they are stored. Sperm entering the caput epididymis are incomplete - they lack the ability to swim forward (motility) and to fertilize an egg. During their transit in the epididymis, sperm undergo maturation processes necessary for them to acquire these functions.[1] Final maturation is completed in the female reproductive tract (capacitation). During ejaculation, sperm flow from the lower portion of the epididymis (which functions as a storage reservoir). They have not been activated by products from the prostate gland, and they are unable to swim, but are transported via the peristaltic action of muscle layers within the vas deferens, and are mixed with the diluting fluids of the seminal vesicles and other accessory glands prior to ejaculation (forming semen). The epididymis possesses numerous, long atypical microvilli. These processes are often called stereocillia; this is incorrect, as they neither contain the microtubular structures of cilia nor function like cilia.[2]

Pathology An inflammation of the epididymis is called epididymitis.

Epididymectomy This is the surgical removal of the Epididymis carried out under local anaesthesia. This is most often performed to relieve pain associated post-Vasectomy. VASA DEFERENTIA: The vas deferens (plural: vasa deferentia), also called ductus deferens, (Latin: "carrying-away vessel"), is part of the male anatomy of some species; they transport sperm from the epididymis in anticipation of ejaculation.

Structure There are two such ducts, connecting the left and right epididymis to the ejaculatory ducts in order to move sperm. Each tube is about 30 centimeters long (in humans) and is muscular (surrounded by smooth muscle), just like the penis. They are part of the spermatic cords.

Function in ejaculation During ejaculation the smooth muscle in the walls of the ductus deferens or vas deferens contracts reflexively, thus propelling the sperm forward. This is also known as peristalsis. The sperm is transferred from the vas deferens into the urethra, collecting secretions from the male accessory sex glands such as the seminal vesicles, prostate gland and the bulbourethral glands, which form the bulk of semen.

Blood supply The vas deferens is supplied by an accompanying artery (artery of vas deferens). This artery normally arises from the inferior vesical artery, a branch of the internal iliac artery. SEMINAL VESICLES: The seminal vesicles (glandulae vesiculosae) are a pair of simple tubular glands posteroinferior to the urinary bladder of males.

Anatomy Each seminal gland spreads approximately 5 cm, though the full length of seminal vesicle is approximately 10 cm, but it is curled up inside of the gland's structure. Each gland forms as an outpocketing of the wall of ampulla of each vas deferens. The excretory duct of seminal gland opens into the vas deferens as it enters the prostate gland.

[edit] Function The seminal vesicles secrete a significant proportion of the fluid that ultimately becomes semen. Lipofuscin granules from dead epithelial cells give the secretion its yellowish color. About 60% of the seminal fluid in humans originates from the seminal vesicles, but is not expelled in the first ejaculate fractions which are dominated by spermatozoa and zinc-rich prostatic fluid. The excretory duct of each seminal gland opens into the corresponding vas deferens as it enters the prostate gland. Prostatic secretion is acidic while seminal vesicle fluid is alkaline, and this results in human semen having a mildly alkaline pH.[1] The alkalinity of semen helps neutralize the acidity of the vaginal tract, prolonging the lifespan of sperm. Acidic ejaculate (pH <7.2) may be associated with blockage of seminal vesicles. The thick secretions from the seminal vesicles contain proteins, enzymes, fructose, mucus, vitamin C, flavins, phosphorylcholine and prostaglandins. The high fructose concentrations provide nutrient energy for the spermatozoa when stored in semen in the laboratory. Spermatozoa ejaculated in the vagina are not likely to have contact with the seminal vesicular fluid but transfer directly from the prostatic fluid into the cervical mucus as the first step on their travel through the female reproductive system. The fluid is expelled under sympathetic contraction of the muscularis muscle coat. In vitro studies have shown that sperm expelled together with seminal vesicular fluid show poor motility and survival, and the sperm chromatin is less protected. Therefore the exact physiological importance of seminal vesicular fluid is not clear. It has been speculated that it is a developmental rest, still seen among some rodents where the last part of the ejaculate form a spermicidal plug which reduces the chances for sperm from a later arriving male to proceed to the oocyte. PROSTATE GLAND:

The prostate (from Greek προστάτης - prostates, literally "one who stands before", "protector", "guardian"[1]) is a compound tubuloalveolar exocrine gland of the male mammalian reproductive system. Females do not have prostate glands. A gland in females with similar characteristics to the prostate, previously called paraurethral or Skene's glands, connected to the distal third of the urethra in the prevaginal space has been considered by a few researchers as a "prostate-like" gland. The prostate differs considerably among species anatomically, chemically, and physiologically.

Function The function of the prostate is to store and secrete a slightly alkaline (pH 7.29) fluid, milky or white in appearance,[2] that usually constitutes 25-30% of the volume of the semen along with spermatozoa and seminal vesicle fluid. The alkalinity of semen helps neutralize the acidity of the vaginal tract, prolonging the lifespan of sperm. The alkalinization of semen is primarily

accomplished through secretion from the seminal vesicles.[3] The prostatic fluid is expelled in the first ejaculate fractions together with most of the spermatozoa. In comparison with the few spermatozoa expelled together with mainly seminal vesicular fluid those expelled in prostatic fluid have better motility, longer survival and better protection of the genetic material (DNA). The prostate also contains some smooth muscles that help expel semen during ejaculation. EJACULATORY DUCT: The Ejaculatory ducts (ductus ejaculatorii) are paired structures in male anatomy, about 2 cm in length. Each ejaculatory duct is formed by the union of the vas deferens with the duct of the seminal vesicle. They pass through the prostate, and empty into the urethra at the Colliculus seminalis. During ejaculation, semen passes through the ducts and exits the body via the penis. Surgery to correct Benign Prostatic Hyperplasia (BPH) may destroy these ducts resulting in retrograde ejaculation. URETHRA:

In anatomy, the urethra (from Greek οὐρήθρα - ourethra) is a tube which connects the urinary bladder to the outside of the body. In males, the urethra travels through the penis, and carries semen as well as urine. In females, the urethra is shorter and emerges above the vaginal opening. The external urethral sphincter is a striated muscle that allows voluntary control over urination. Male urethra

In the human male, the urethra is about 8 inches (20 cm) long and opens at the end of the penis. The urethra provides an exit for urine as well as semen during ejaculation. The urethra is divided into four parts in men, named after the location: Region

Description

This is the intramural part of the urethra and pre-prostatic varies between 0.5 and 1.5 cm in length urethra depending the fullness of the bladder.

prostatic urethra

Epithelium

Transitional

Crosses through the prostate gland. There are several openings: (1) the ejaculatory duct receives sperm from the vas deferens and ejaculate fluid from the seminal vesicle, (2) several prostatic ducts where fluid from the Transitional prostate enters and contributes to the ejaculate, (3) the prostatic utricle, which is merely an indentation. These openings are collectively called the verumontanum.

A small (1 or 2 cm) portion passing through the external urethral sphincter. This is the narrowest membranou part of the urethra. It is located in the deep s urethra perineal pouch. The ducts of the bulbourethral glands (Cowper's gland) enter here.

Pseudostratified columnar

Runs along the length of the penis on its ventral (underneath) surface. It is about 15–16 cm in length, and travels through the corpus spongiosum. The ducts from the urethral gland (gland of Littre) enter here. Some textbooks will subdivide the spongy urethra into two parts, the bulbous and pendulous urethra.

Pseudostratified columnar – proximally, Stratified squamous – distally

spongy urethra (or penile urethra)

The length of a male's urethra, and the fact it contains a prominent bend, makes catheterization more difficult. The integrity of the urethra can be determined by a procedure known as retrograde urethrogram. BULBOURETHRAL GLANDS: A bulbourethral gland, also called a Cowper's gland for anatomist William Cowper, is one of two small exocrine glands present in the reproductive system of human males. They are homologous to Bartholin's glands in females.

Location Bulbourethral glands are located posterior and lateral to the membranous portion of the urethra at the base of the penis, between the two layers of the fascia of the urogenital diaphragm, in the deep perineal pouch. They are enclosed by transverse fibers of the sphincter urethrae membranaceae muscle.

[edit] Structure The bulbourethral glands are compound tubulo-alveolar glands, each approximately the size of a pea. They are composed of several lobules held together by a fibrous covering. Each lobule consists of a number of acini, lined by columnar epithelial cells, opening into a duct which joins with the ducts of other lobules to form a single excretory duct. This duct is approximately 2.5 cm long and opens into the urethra at the base of the penis. The glands gradually diminish in size with advancing age.[1]

[edit] Function During sexual arousal each gland produces a clear, viscous secretion known as pre-ejaculate. This fluid helps to lubricate the urethra for spermatozoa to pass through, it neutralizes traces of acidic urine in urethra[2], and helps flush out any residual urine or foreign matter. It is possible for this fluid to pick up sperm, remaining in the urethral bulb from previous ejaculations, and carry them out prior to the next ejaculation. The Cowper's gland also produces some amount of

prostate specific antigen and Cowper's tumors may increase PSA to a level that makes prostate cancer suspicious.